Homocysteine with Liberation of Hydrogen Sulfide

Other observations show the existence of such a transformation beyond any doubt. Such is the work by Brand, Cahill, and Block (2G) cited above, according to whom the sulfur of homocysteine ingested by a patient suffering from cystinuria is excreted for the largest part in the form of extra cystine. 

Among the theories proposed to explain the formation of cysteine from homocysteine, the one by Brand, Block, Kassell, and Cahill (25) 

The over-all results of the work of du Vigneaud and his collaborators, describing the synthesis of cysteine from methionine sulfur in higher animals, is shown in the following scheme.  

The validity of this mechanism is further confirmed by the observations of Stetten (117), who fed rats a diet containing serine with isotopic nitrogen, and found that after three days the cystine in the tissue proteins is particularly rich in labeled nitrogen, thus furnishing the proof for the transfer of the carbon chain from serine to cystine. 

Cysteine thus appears both as a primary substance of animal metabolism, and as an intermediary substance in the transformations of the sulfur initially furnished by methionine. 

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B. Desulfuration of Homocysteine with Liberation of Hydrogen Sulfide 379... 

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